Gas turbine lubricants

ABSTRACT

A gas turbine lubricant having excellent high temperature stability and additive compatibility can be formulated by employing, as a base stock, a blend of a carboxylate ester, and a low viscosity mineral oil.

United States Patent [191 Anzenberger, Sr.

[4 1 Oct. 14, 1975 GAS TURBINE LUBRICANTS [75] Inventor: Joseph F. Anzenberger, Sr., New

City, NY.

[73] Assignee: Stauffer Chemical Company,

Westport, Conn.

[22] Filed: Aug. 7, 1972 [21] Appl. No.: 278,519

[52] US. Cl 252/47.5; 252/50; 252/56 R;

3,236,774 2/1966 Thompson et al..... 252/56 S 3,337,457 8/1967 Fowler et al 252/56 S 3,376,224 4/1968 Elliott et al. 252/47.5

FOREIGN PATENTS OR APPLICATIONS 1,031,106 5/1966 United Kingdom UI'HER PUBLICATIONS Murphy et al., Ind. & Engineering Chem., Vol. 42, (1950), pp. 2415-2420. Atkins et al., Ind. Eng. Chem., April, 1947, pp. 491-497. Adamczak et al., Ind. Eng. Chem., Jan. 1964, pp. 40-47.

Gunderson et 211., Synthetic Lubricants, 1962, pp. 165-169.

Primary Examiner-Delbert E. Gantz Assistant Examiner-I. Vaughn Attorney, Agent, or FirmChar1es B. Rodman [57] ABSTRACT A gas turbine lubricant having excellent high temperature stability and additive compatibility can be formulated by employing, as a base stock, a blend of a carboxylate ester, and a low viscosity mineral oil.

15 Claims, N0 Drawings GAS TURBINE LUBRICANTS BACKGROUND OF THE INVENTION Synthetic ester lubricants have replaced common lubricating oils, such as mineral oils, in many functional fluid applications due to their superior oxidative, thermal and volatility characteristics under service conditions. This is particularly true in the field of automotive, marine and stationary gas turbine lubricants where the operating conditions are extremely severe. Suitable gas turbine lubricants must exhibit a high degree of fluidity at low temperatures, and low volatility and sufficient lubricity at high temperatures. Thus, gas turbine lubricants should have a viscosity of less than about 20,000 centistokes at 25 F., less than about 2,000 centistokes at F. and in the range from about 5.0 to about 7 centistokes at 210 F. Similarly, a flat viscosity temperature curve, i.e., a high viscosity index, is desirable since proper lubrication in most applications requires that the lubricant be adaptable to changes in temperatures without extreme variations in viscosity. Other essential properties which a gas turbine lubricant must possess include load carrying ability, hydrolytic and oxidative stability, low wear and anti-corrosion characteristics, additive compatibility, and seal compatibility. It is also desirable that these lubricants be relatively inexpensive in order to be commercially attractive for industrial use.

Perhaps the most critical of the above described characteristics, at least insofar as the selection of suitable base stocks for turbine applications is concerned, are the low and high temperature viscosities and high temperature oxidative and thermal stability. Thus, while the temperature viscosity characteristics of the base stock may be varied somewhat by the addition of known viscosity index (V.l.) improvers, the base stock material itself must, in the first instance, possess viscosities which are sufficiently close to the viscosity requirements of that particular application as to be within the correctable range of V.l. improver and, secondly, they must be compatible with the V.l. improver. It is to be understood, of course, that base stocks having the proper viscosity-temperature characteristics without the addition of V.I. improvers would be particularly preferred. Likewise, the base stock should be sufficiently responsive to the antioxidants commonly employed in turbine lubricants to give fluids capable of withstanding the high temperatures encountered in modern gas turbines without acid buildup, viscosity change or coke formation.

The prior art has attempted to satisfy these strict requirements by employing a variety of petroleum oils. These materials have proven to be too thermally and oxidatively unstable, however, to withstand the extreme conditions found in turbine applications. While their performance can be somewhat improved by the addition of large amounts, i.e., up to about by weight, of additives, these petroleum oils are generally unsatisfactory for use as gas turbine lubricants.

Various synthetic esters have been used as base stocks for gas turbine lubricants. For example, the prior art has suggested the use of aliphatic esters of dicarboxylic acids, such as the diesters off adipic or sebacic acid, as lubricants for gas turbine applications. While the dialkyl adipates have good low temperature viscosities, their high temperature viscosity is so low that they can only be used in combination with relatively large amounts of V.I. improvers. Furthermore, these adipates exhibit very poor oxidative stability, even when combined with conventional antioxidants, under normal operating conditions. Finally, the dialkyl adipates have a tendency to thermally degrade, thereby making them less suitable for gas turbine lubricants.

In an attempt to solve the thermal degradation problem, US. Pat. No. 2,936,320, filed June 24, 1957, in the name of George J. Benoit, Jr., teaches the use of a mixture of isophthalic/terphthalic acid esters of a mixture of C alcohols. These materials, however, normally have poor viscosity indexes, and are too viscous at low temperatures.

Therefore, it is an object of the present invention to provide functional fluid base stocks which possess all of the beneficial characteristics described above.

It is a further object of the present invention to provide base stocks suitable for use in gas turbine lubricants.

Another object of the present invention is to provide gas turbine lubricant base stocks which have excellent low and high temperature viscosities, which are combinable with known antioxidants to yield fluids of exceptional thermal and oxidative stability, and which are relatively inexpensive to produce. Other objects will become apparent from the disclosure contained hereinafter.

It has now been discovered that the objects of the present invention can be accomplished by employing a new class of base stocks comprised of a combination of carboxylate ester and a low viscosity mineral oil. Furthermore, it has been discovered that exceptional gas turbine lubricants can be formulated by incorporating into the above described base stocks an antioxidant package comprising a phenothiazine or a substituted phenothiazine in combination with a diaryl amine. This combination can also contain a methylene-linked hindered bisphenol.

An essential component of the base stocks of the present invention is a carboxylate ester. The term carboxylate ester as used herein is meant to designate those esters selected from the group consisting of the diesters of aliphatic or aromatic dicarboxylic acids and monohydric alcohols, and the monocarboxylic acid esters of dihydric or polyhydric alcohols. These materials are well known in the art and are illustrated by the following: the diesters of malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic, maleic, fumaric acids and phthalic and isophthalic acid; the dicarboxylic acid esters of butylene glycol; the monocarboxylic acid esters of trimethylol ethane, trimethylol propane, pentaerythritol and dipentaerythritol. When an aliphatic dicarboxylic acid is used to make the synthetic ester, the monohydric alcohol moiety of these esters normally has from 4 to 20 carbon atoms and preferably from 6 to 13 carbon atoms. Mixtures of these esters can also be used. Likewise when a dihydric or polyhydric alcohol is used to prepare the synthetic ester, the monocarboxylic acid has from 2 to 20 and, preferably, 4 to 12 carbon atoms. Mixtures of these esters can also be used.

While any of the above described synthetic esters can be used in combination with the mineral oil described hereinafter to form the base stocks of the present invention, certain of these carboxylate esters have been found to be preferred. Thus, the isophthalate esters of C to C monohydric alcohols and the trimethylolpropane, trimethylol ethane and pentaerythritol esters of C to C monocarboxylic acids have been found to be particularly compatible with the mineral oils of the present invention.

i COR wherein R and R are the same or different and are primary or secondary alkyl groups having from 4 to carbon atoms, and preferably, from 6 to 13 carbon atoms. The alkyl groups can be derived from primary or secondary alcohols and can be straight or branched chain. The diesters can be made from pure isophthalic acid or prepared from a crude commercial grade of isophthalic acid, i.e., containing up to about 15 percent by weight of a terphthalic acid.

Illustrative of the alkyl radicals R and R are the following: normal butyl, isobutyl, secondary butyl, normal amyl, isoamyl, 2-methylbutyl, 2,2-dimethyl propyl, 1- methyl butyl, l,2-dimethyl propyl, normal hexyl, 1- methylamyl, Z-ethyl butyl, 1,2,2-trimethyl propyl, 3,3- dimethyl butyl, Z-methyl amyl, l-ethyl Z-methyl propyl, 1,3-dimethyl butyl, isohexyl, 3-methylamyl, 2-ethyl butyl, normal heptyl, 1,2,3-trimethyl propyl, 1,2,2- trimethyl butyl, l-isopropyl 2-methyl propyl, l-methyl 2-ethyl butyl, 2-methyl hexyl, l-isopropyl butyl, l-ethyl 3-methyl butyl, 1,4-dimethyl amyl, isoheptyl, l-ethyl Z-methyl butyl, l-methyl hexyl, l-propyl butyl, normal octyl, l-methyl heptyl, 2,2,3,3-tetramethyl butyl, 2- ethyl hexyl, 6-methyl heptyl (iso-octyl), normal nonyl, l-methyl octyl, l-ethyl heptyl, 7-methyl octyl, 3,5,5- trimethyl hexyl, 3,5-dimethyl heptyl, normal decyl, 1- propyl heptyl, 2-is0propyl S-methyl hexyl, lauryl, undecyl and C C alkyl groups. This list is illustrative only and is not intended to be all inclusive.

Even among the preferred isophthalate esters, certain esters when employed to form base stocks according to the present invention, yield basestocks having exceptional thermal and oxidative stability, and temperature-viscosity characteristics, even as compared to other base stocks within the scope of the present invention. The most preferred isophthalate esters are those wherein R, and R can each be C C alkyl groups, such as n-hexyl, n-heptyl, n-octyl, Z-ethylhexyl, n-nonyl, isononyl, n-decyl, isooctyl and isodecyl. These preferred isophthalates include diisooctyl isophthalate, di-2-ethylhexyl isophthalate, n-octyl n-decyl isophthalate, isooctyl isodecyl isophthalate, 2-ethylhexyl isodecyl isophthalate, diisodecyl isophthalate and esters of isophthalic acid with mixtures of C -C straight chained alcohols. The mixed isophthalates are intended to cover those esters having each of the alkanol moieties present in varying amounts and notjust in a 50:50 relationship with the other alkanol.

It has further been discovered that improved base stocks having excellent viscosity, additive compatibility and oxidative and thermal stability characteristics can be formulated by substituting an adipate ester for a portion of the preferred isophthalate ester 'in the base stocks disclosedabove. These materials exhibit excellent low temperature viscosity characteristics. Thus, up to about 20% by weight of the isophthalate can be replaced with an adipate ester derived from the esterifi- Cation of adipic acid with a C C alkanol or mixture of C -C alkanols. Consequently, another preferred embodiment of the present invention comprises gas turbine lubricant base stocks containing a blend of an isophthalate ester of a C C alcohol, an adipate ester of a C -C1" alcohol and a low viscosity mineral oil. While the adipates can be used in combination with any of the isophthalates discussed above, they are most beneficially used with isophthalates having relatively high viscosities. For example, base stocks formulated with a mineral oil and a combination of di-Z-ethylhexyl isophthalate and a mixed octyl decyl adipate are significantly better in low temperature viscosity properties than are the base stocks formulated from the same mineral oil and di-Z-ethylhexyl isophthalate alone.

The preferred trimethylol propane, trimethylol ethane and pentaerythritol esters for use in the present invention are those having a formula corresponding to:

inodR 0 ll R;,- ch,ocR,

0 ll mock,

wherein R is selected from the group consisting of methyl, ethyl and and each of R R R and R are branched or straight chained alkyl groups having from 3 to l 1 carbon atoms. These'materials can also be crosslinked by partial esterification with a dicarboxylic acid such as azelaic acid as is well known in the art. It will also be appreciated by those skilled in the art that the preferred pentaerythritol esters will normally contain minor amounts of diand tri-pentaerythritol esters. Particularly preferred trimethylol propane and pentaerythritol esters for use in the present invention are trimethylol propane triheptanoate and pentaerythritol triheptanoate monobutyrate crosslinked with azelaic acid.

While the above described isophthalate, trimethylol ethane, trimethylol propane and pentaerythritol esters are generally preferred for use in the base stocks of the present invention, it has further been discovered that in those situations where the final lubricant must exhibit exceptional low temperature properties, the diesters of 1,3-butylene glycol and/or neopentyl glycol with monocarboxylic acids having from 6 to 20 carbon atoms are particularly preferred for blending with the mineral oils according to the present invention. Particularly preferred in this regard is 1,3-butylene glycol pelargonate heptanoate.

The other essential component for the base stocks of the present invention is a low viscosity mineral oil. The low viscosity mineral oils which are suitable for use in the present invention are highly paraffinic and/or naphthenic oils having a minimum amount of unsaturation and are well known in the refining art. They are produced from crude oils by subjecting the crude oil to a first distillation under ordinary pressures to remove the low boilers, and a second steam distillation to remove heavy oil and waxy fractions. The resultant material is then deasphalted, dewaxed, treated with solvents and clays.

The low viscosity mineral oils of the present invention are further characterized by having a viscosity of 210 F. of from about 5 to about centistokes and preferably from about 5 to about 6.5 centistokes. Typical properties for the low viscosity mineral oils of the present invention are listed in Table l.

porating therein an effective amount of any of the well known antioxidants such as phenothiazine, the derivatives of phenothiazine, the secondary diaryl amines or the hindered phenols. It is to be appreciated that the above list is intended as illustrative only and the present invention in its broadest aspect is not limited thereto. These antioxidants can be incorporated into the base stocks in amounts ranging from about 0.1 to about 10% by weight of the entire formulation. For most applications, however, it is preferred that the antioxidant be present in an amount from about 0.5 to about 5% by weight of the entire formulation.

While the present invention in its broadest aspects relates to functional fluid base stocks as described above, it has been found that by incorporating particular antioxidants into these base stocks, fluids having exceptional high temperature stability can be obtained. Therefore, the present invention also relates to func- TABLE 1 Oil A Oil B Oil C Oil D Oil E Oil F Oil G Viscosity (centistokes) at lO0F 33 42 32 39.7 45.2 33.2 42.5 at 210F 5.! 6.4 5.07 5.55 6.38 5.9 6.2 Flash Point F 4l5 455 390 410 415 400 440 Fire Point "F 450 490 Pour Point F O 0 5 5 0 5 10 Typical analysis for the low viscosity mineral oils of the present invention are given in Table II.

TABLE [I Oil A Carbon Analysis Aromatic Carbon 4 4 Naphthenic Carbon 71 28 27 Parafflnic Carbon 7! 68 69 Molecular Type Analysis (Clay-Gel) Asphaltenes, Wt.% 0 0 Polar Compounds, Wt.% 0.3 0.3 Aromatics, Wt.% 12.7 l3.5 Saturates, Wt.% 87.0 86.2 Aniline Point "F Z2l 226 The preferred low viscosity mineral oils for use in the present invention are the so called white mineral oils due to their exceptional additive compatibility. The term white mineral oil as used herein is meant to designate those low viscosity mineral oils having unsulfonated residues of not less than 99%.

The carboxylate ester and the low viscosity mineral oil can be blended over a relatively broad range to yield gas turbine lubricant base stocks possessing excellent viscosity, additive compatibility and oxidative and thermal stability characteristics. Normally from about to about 80% by weight of the base stock of carboxylate ester is blended with from about 80 to about 20% by weight of the mineral oil. Preferably from about 50 to about 80% by weight, and most preferably from about 60 to about 80% by weight of the base stock is comprised of carboxylate ester with the remainder being mineral oil.

The base stocks of the present invention have been found to be responsive to those antioxidants commonly employed in gas turbine lubricants and hydraulic fluids. Thus, the base stocks of the present invention are rendered oxidatively stable at high temperatures by incortional fluids comprising the base stocks described above and certain antioxidants, which have been found to be particularly effective in stabilizing these base stocks against oxidative degradation at high temperatures. In particular, the narrower embodiment of the present invention can be said to relate to functional fluids comprising l) a base stock made up of a blend of a carboxylate ester and a low viscosity mineral oil as described above and (2) a binary antioxidant combina-,

tion of (a) phenothiazine or a derivative of phenothiazine and (b) a secondary diaryl amine. The term derivative of phenothiazine, as used herein and in the claims is meant to designate N-alkyl phenothiazines and the monoand dialkyl substituted derivatives of both phenothiazine and the N-alkyl phenothiazines wherein the alk yl groups have from 1 to 20 carbon atoms. Illustrative of these derivatives of phenothiazine are N-ethyl phenothiazine, dioctyl phenothiazine and N-ethyl dioctyl phenothiazine. The term diaryl amine as used herein is meant to designate diphenyl amine, the phenyl naphthylamines and the monoand dialkyl derivatives of diphenyl amine and the phenyl naphthylamines, wherein the alkyl groups have from 1 to 20 carbon atoms. Illustrative of secondary diaryl amines are diphenyl amine, p,p-dioctyl diphenyl amine, phenyl-anaphthylamine and p-tert-octylphenyl-anaphthylamine. A particularly preferred binary antioxidant for use in the present invention is the combination of N-ethyl dioctyl phenothiazine and p,p'-dioctyl diphenyl amine. Normally the binary antioxidant will contain from about 0.5 to about 5% by weight of the final formulation of each of the components, and preferably from about 0.5 to about 2% by weight of each.

It has further been discovered that the cost of the formulations described above can be reduced, while maintaining or improving their excellent oxidative stability, by substituting a less expensive methylene-linked hindered bisphenol, such as a methylene bis(di-t-alkyl phenol), for a portion of the relatively expensive phenothiazine or phenothiazine derivative. While the bisphenol can be used in amounts from about 0.05 to about by weight, a particularly preferred ternary antioxidant combination comprises (a) 0.52% by weight of N-ethyl dioctyl phenothiazine, (b) 0.5-2% by weight of p,p-dioctyl diphenyl amine and (c) 0.1 to 2% by weight of 4,4'-methylene bis(2,6-di-t-butyl phenol).

While the base stocks of the present invention have excellent viscosity properties by themselves, it is often advantageous to blend in a V.l. improver. Thus, any of the well known V.l. improvers such as the polymers and copolymers of esters of acrylic and methacrylic acid with C -C alcohols can be blended with the base stocks of the present invention with little or no phase separation. These acrylates and methacrylates normally have a molecular weight in the range of from about 4,000 to about 20,000. Typical of these acrylates and methacrylates are those sold commercially under the trademark Acryloid by Rohm and Haas. Other V.l. improvers which can be employed with the base stocks of the present invention include polyalkylene glycols, high molecular weight polyesters, high molecular weight polyalkanes, such as poly-n-decane, polyolefins, such as the polyisobutylenes, and copolymers of styrene with the above described acrylates and methacrylates all of which are well known in the art. While these V.l. improvers can be employed in amounts up to about by weight of the final formulation, one of the particular advantages of the base stocks of the present invention resides in the fact that they require little, if any, V.l. improver to bring them within the ranges established for gas turbine applications. Thus, while petroleum oils normally require 5 to by weight of the final formulation of a V.l. improver to meet gas turbine specifications, the base stocks of the present invention normally use less than 5% and preferably less than 2.5% V.l. improver and still meet gas turbine specifications.

The lubricants of the present invention can additionally contain any of the well known lubricity and extreme pressure (E.P.) additives such as the organic phosphites, phosphonates, phosphates and thereof. Particularly useful E.P. additives include the alkyl or aryl hydrogen phosphonates and the amine salts of dialkyl phosphorous acid esters. Triaryl phosphates, and particularly tricresyl phosphosphates, have been found to be preferred as a lubricity additive for most gas turbine lubricants. These HP. and lubricity additives are normally employed in amounts from about 0.1 to about 5% by weight of the entire lubricant formulation.

Lubricants containing the base stock of the present invention can also contain any of the well known metal salts deactivators such as benzotriazole, tolyltriazole, N,N'- disalicylidenedialkyl amines and sebacic acid. Particularly preferred for the present invention are benzotriazole and sebacic acid. These additives are normally added in amounts from about 0.005 to about 1.0% by weight of the entire formulation.

Likewise, antifoaming agents can also be incorporated into lubricants containing the base stock of the present invention. Typical of these additives are the silcone type antifoamants such as the methyl silicones and siloxanes. They are normally employed in amounts from about 0.0001 to about 0.002% by weight of the entire formulation.

The present invention will be further illustrated by the following examples. All quantities are given as parts by weight unless otherwise designated.

EXAMPLE 1 Viscosity (centistokes) at 210 F. 5.80 at 100 F. 31.39 at 0 F. 1,017 Viscosity Index 141 EXAMPLE 2 parts by weight of a mixed ester of isophthalic acid and a commercially available mixture of a C C straight chained alkanols having 24.5% C 38% C 32.5% C and 0.75% C alkanol content is blended with 50 parts by weight of Oil E of Table l. The resultant blend has the following viscosity characteristics:

Viscosity (centistokes) at 210 F. 5.05 at 100 F. 29.68 Viscosity Index 106 These base stocks when formulated with conventional additives give excellent thermal and oxidative stability as compared to those base stocks used previously.

EXAMPLES 3-21 A series of gas turbine lubricants are formulated according to Table 3.

TABLE 3 Example No. 3 4 5 i 6 7 8 '9 10 11 12 lsophthalale di2-ethylhexyl isophthalate 61.405 53.615 45.425 36.826 36.826 61.40 61.305 61.305 61.45 53.615 A ipate isooctyl isodecyl adipate (:20) molar 13.55 11.84 10.02 8.128 8.128 13.55 13.35 13.50 13.50 11.84 di-Z-ethylhexyl adipate Oils (Table 1) A 3000* B 20.00

C D 50.00 20.00 l1:; 20.00 30.00 40.00 50.00 20.00 21.00 G H TABLE 3 -Continued Example 3 4 s 6 7 s 9 10 u 12 Additives polymethacrylate V.l. improver 1.50 1.00 1.00 1.00 1.00 1.50 1.00 1.00 (Rohm & Haas Acryloid 707) polyisobutylene V.l. improver 1.50 1.50 (Amoco 600) N-ethyl dioctyl phenothiazine 1.25 l 25 1.25 1.25 1.50 1.25 1.25 1.25 1.25 p.p'-dioctyl diphenyl amine 1.25 1.25 1.25 1.25 1.50 1.25 1.25 1.25 1.50 1.25 4.4'-methylene bis(2.6-di-t- 0.50 0.50 0.50 0.50 0.50 0.50 0.05 0.50 0.50 0.50 butyl phenol) benzotriazole 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 sebacic acid 0.025 0.025 0.025 0.025 0.025 0.025 0.02 0.025 0.025 0.025 tricresyl phosphate 0.50 0.50 0.50 0.50 0.50 0.50 0.05 0.50 0.50 0.50 Lubrizol L2 762 styrenated phenyl-B-naphthylamine 1.50 Example No. 13 14 15 16 17 l8 I9 20 21 lsophthalate di-2-ethylhexyl isophthalate 45.425 62.425 61.872 61.405 61.405 61.405 36.826 36.826 61.405 Adipate isooctyl isodecyl adipate (80:20) molar 10.02 13.778 13.733 8.628 8.628 di-Z-ethylmexyl adipate 13.55 13.55 13.55 13.55 Oils (Table l) 4000* 20.00 50.00

A B C D 20.00 E 20.00 F 20.00 50.00 20.00 G 20.00 H Additives polymethacrylate V.l. improver 1.00 1.00 1.50 1.50 1.50 1.00 1.00 1.50 (Rohm & Haas Acryloid 707) polyisobutylene V.l. improver 1.50 (Amoco 600) N-ethyl dioctyl phenothiazine 1.25 0.85 1.25 1.25 1.25 1.25 1.25 1.25 p,p'-dioctyl diphenyl amine 1.25 1.25 1.00 1.25 1.25 1.25 1.25 1.25 1.25 4.4-methylene bis(2.6-di't- 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 butyl phenol) benzotriazole 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 sebacic acid 0.025 0.025 0.025 0.025 0.025 0.025 0.025 0.025 0.025 bricresyl phosphate 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 Lubrizol LZ 762** styrenated phenyl-Bmaphthylamine 0.50 the oil used is a hydrogcnatcd mineral oil having a 210 F. viscosity of 4 ccnlistokcs and a 100 F. viscosity of 22.8. "a commercial friction modifier available from Luhrizol.

Viscosity characteristics for a representative samted to Corrosion and Oxidation Stability Test FSTM pling of the gas turbine lubricants of Table 3 are given 791B at 347 F. for 72 hours with an air flow rate of 5.0 m Table 4. Certain of the fluids of Table 3 are submitliters air/hours. The results are contained in Table 5.

TABLE 4 Example N0. 3 4 5 6 7 8 10 11 12 13 Viscosity (centistokes) at 210: 5.70 5.43 5.59 5.81 5.75 5.46 5.15 5.43 4.77 4.71 at 100 l-. 36.54 35.04 36.66 38.45 38.05 34.32 32.76 34.87 27.79 26.78 at 25 F. 6,850 4.836 11.398 6,876 6.814 Viscosity Index 104 98 98 101 100 104 92 99 100 102 TABLE Example No. 3 4 5 6 7 11 12 Viscosity Change 5.2 6.5 6.9 4.4 7.5 7.0

1% at 100 F.) 88

Acid No. Change 1.02 1.02 1.10 0.86 1.53 1.28 1.71 1.58

Metal Weight Change Mg Nil Nil Nil Nil Nil 0.04 Nil Nil Steel Ni 0.02 0.02 Nil 0.04 0.06 0.02 Nil A1 Nil 0.02 Nil 002 0.04 0.04 Nil Nil Ag 0.02 Nil 0.10 0.07 0.04 0.02 Nil Nil Cu 0.02 Nil 0.02 0.02 0.04 0.08 0.04 0.04

Example 130 14 16 17 19 21 iscosity ange 8.0 9.1 7.1 11.01 12.2 13.

(7: at F.) 2 844 Acid No. Change 1.42 1.47 1.98 1.01 2.38 1.89 3.24 2.23

(mg KOH/g) Metal Weight Change (mg/ m Mg Ni] 0.04 0.02 0.02 0.02 Nil 0.02 Nil Steel 1 1 0.04 0.02 v Nil 0.04 Nil Nil 0.02 Nil A1 0.02 Nil Nil 0.02 Nil Nil 0.02 Nil Ag -0.02 -O 20 O.16 Nil ().()4 0.10 O 10 0.04

Cu Nil Nil Nil Nil 0.04 0.02 0:02 -0.08

porating therein an additional small amount viscosity index improver. Table demonstrates the exceptional oxidative stability of the gas turbine lubricants of the present invention. More specifically, while viscosity 5 changes of up to in the 347 F. Corrosion and Oxi- TABLE 6 Example No. 3 4 6 8 9 l0 16 17 18 Viscosity Change 21.8 24.1 23.2 23.7 23.3 26.2 24.3 23.3 28.9 (9? at 100 F.) Total Acid No. 580 6.35 10.12 8.78 5.56 8.39 7.57 5.56 10.25 Change (mg KOH/ gm.) Metal Weight Change (mg/cm) Mg Nil 0.02 0.40 Nil 0.02 0.08 0.020 0.02 Nil Steel 0.04 0.06 0.37 Nil 0.04 Nil Nil 0.03 Nil A1 Nil 0.08 0.37 0.015 Nil 0.04 Nil Nil 0.015 Ag -0.08 0.02 0.28 0.04 0.06 0.04 0.08 0.05 0.10 Cu -0.06 0.0 0.41 -0.08 0.04 0.06 -0.l7 0.08 0.l39

The foregoing data clearly demonstrates that the base stocks of the present invention yield gas turbine lubricants which possess excellent viscosity and stabil dation Stability Test are acceptable, the lubricants of the present invention generally exhibit viscosity changes of less than 10%.

ity characteristics. In particular, Table 4 demonstrates that each of the fluids tested, with the exception of Examples 12 and 13, meet the normal viscosity requirements for gas turbine lubricants. In the case of Exam- EXAMPLES 22-31 A series of gas turbine lubricants which do not conples 12 and 13, the 210 F. viscosities of these materials tain a viscosity index improver are formulated accord can readily be adjusted to above 5 centistokes by incoring to Table 7.

TABLE 7 EXAMPLE NO. 22 23 24 25 26 27 28 i 29 30 31 Carboxylate Ester PE 1 47.852 1 47.852 PE 2 37.148 37.148 61.628 37.164, 37.164 PE 3 I 47.852 Trimethylol propane tri- 9.287 9.287 15.470 9.291 44.955 heptanoate I 47.852

1,3-butylene glycol'pelargonate heptanoate di-Z-ethylhexyl adipate v 9.291 1 l Oils 47.852* 47.852* 47.852* 47.852*

Additives N-ethyl dioctyl phenothiazine 1.25 1.25 1.25 0.50 0.50 0.50 p,p'-diocty1 diphenyl amine 1.25 1.25 1.00 1.25 1.25 1.25 1.50 1.50 1.50 1.50 4,4'-methy1ene bis(2,6-dit-butyl phenol) 0.50 0.50 0.50 0.50 0.50 0.50 0.50 octylphenyl-a-naphthyl amine 1.50 1.50 1.50 1.50 phenyl-a-naphthyl amine 1.50 1.50 1.15

benzotriazole 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 sebacic acid 0.025 0.025 0.025 0.025 0.025 0.025 0.025 0.025 0.025 0.025 tricresyl phosphate 0.50 0.50 0.50 0.50 0.50 0.50 0.50 tricresyl/trixylyl phos- 0.27 0.27 0.27

phate pour point depressant 0.25 0.25 0.25

(Lubrizol 3123) Viscosity (centistokes) at 210F 5.41 5.13 5.31 5.55 5.29 5.65 4.30 4.33 4.28 2.88 at F 33.27 29.98 29.85 33.98 31.11 31.52 23.01 23.25 22.73 11.41 25F 1,803 1.507 1,079 3,989 5.197 5,115'

at 0F 204 Oxidation Corrosion Test at 347F Viscosity Change 12.9 16.4 7.6 7.4 5.9 10.8 12.2 12.9 8.5 Acid No. Change (mg KOH/g) 1.08 1.80 1.18 1.20 0.94 1.00' 1.14 1.60 1.45 Metal Weight Change (mg/cm) Mg 1 1 Nil Nil 0.06 -0.02 0.04 Nil 0.04 0.02 Nil Steel -0.02 0.04 0.04 0.02 -0.04 Nil 0.02 0.02 Nil Al 0.04 0.04, 0.02 Nil -0.02 .Nil 0.02 Nil Nil TABLE 7 -Continued EXAMPLE NO. 22 23 24 25 26 27 28 29 30 3| Ag -0.04 0.02 -0.04 0.04 0.08 0.06 0.06 0.06 0.04 Cu "0.06 0.06 -0.02 0.02 -().()4 Nil Nil {).02 0.02 at 400F Viscosity change ('71) 32.2 55.7 30.7 Acid No. Change (mg KOH/g) 3.35 8.35 l2.35 Metal Weight Change (mglcm Mg 0.02 Nil 5.52 Steel Nil Nil 0.06 Al Nil Nil 0.02 Ag -0.08 0.07 Nil Cu 0.l7 0.08 0.l6

PE l cstcrification product of 1 part pentacrythritol with 2.6 parts n-hcptunoic acid. 0.4 parts nco-hcptanoic acid and L parts n-hutyric acid. "'PE 2 pentacrythritol monobutyratc lrihcptanoatc crosslinkcd with 3 molar 71 azclaic acidv "PE 3 estcril'icution product of I part pentacrythritol with 2.45 parts n-hcxanoic acid. 0.8 parts of a mixture of uctanoic and dccanoic acid and 0.75 parts "Hydrogenated Sunpar llO". a commercial paraffinic base stock sold by Sun Oil Company.

COR

wherein R and R are each a primary or secondary alkyl group having from 4 to 20 carbon atoms and (ii) an adipate ester derived from the esterification of adipic acid with C -C alkanols, wherein the combination of esters are present in lubricating amounts and the isothalate ester consists of at least 80% by weight of the combination; and

b. from about 80 to about 20% by weight of the base stock of a low viscosity mineral oil having a viscosity in the range from about to about centistokes at 210F.

2. The base stock of claim 1 wherein said isophthalate ester is present in an amount from about 50 to about 80% and said oil is present in an amount from about 50 to about by weight of the base stock.

3. The base stock of claim 1 wherein R and R are each a C -C alkyl group.

4. The base stock of claim 3 wherein said adipate diester is derived from the esterification of adipic acid and an 80:20 molar mixture of isooctanol and isodecanol.

5. The base stock of claim 1 wherein said adipate diester is di-2-ethylhexyl adipate.

6. The base stock of claim 1 wherein said isophthalate ester is selected from the group consisting of di-2- ethylhexyl isophthalate, diisooctyl isophthalate, isooctyl isodecyl isophthalate, 2-ethylhexyl isodecyl isophthalate, diisodecyl isophthalate, and the ester of isophthalic and mixtures of C C straight chained alkanols.

7. The base stock of claim 6 wherein the isophthalate ester is di-Z-ethylhexyl isophthalate.

8. The base stock of claim 1 wherein said mineral oil has a viscosity in the range from about 5 to about 6.5 at 210 F.

9. A gas turbine lubricant comprising the base stock of claim 1 and up to 5% by weight of the lubricant of a viscosity index improver.

10. A gas turbine lubricant consisting essentially of the base stock of claim 1 and an oxidation inhibiting amount of a combination of (a) phenothiazine or derivative of phenothiazine and (b) a secondary diaryl amine.

11. The gas turbine lubricant of claim 10 wherein said derivative of phenothiazine is N-ethyl dioctyl phenothiazine and said diaryl amine is p,p'-dioctyl diphenyl amine.

12. The gas turbine lubricant of claim 10, which additionally contains an oxidation inhibiting amount of a methylene-linked hindered bisphenol.

13. The gas turbine lubricant of claim 12 wherein said methylene-linked hindered bisphenol is 4,4- methylene bis(2,6-di-t-butyl phenol).

14. The base stock of claim 6 wherein said isophthalate ester is derived from isophthalic acid and a mixture of C -C straight chained alkanols.

15. The base stock of claim 6 wherein said isophthalate ester is derived from isophthalic acid and a mixture of C,,C, straight chained alkanols.

UNITED STATES PATENT AND TRADEMARK OFFICE QEHHQATE 0F REUHN Q PATENT NO. 3912 6 10 DATED October 14, 1975 INVENTOR(S) Joseph F, Anzenberger, Sr.

It rs certified that error appears in the ab0ve-derxtified pares? and that sard Letters Patent are hereby corrected as shown below:

Column 1, line 64, the word off should read --of-=- Column 5, line l l, the word of should read ---at- 0 Column 9, underneath the adipate" listings, the

term 'di--2-ethylmexyl adipate" should read --di-=2ethylhexyl adipate-- Table 5, bridging columns9 and 10 in the entry for Q 1' "oils" (Table l), the values "20, OO" and "50a 00" should correspond to the "A" oil.

In Table 3, bridging columns 9 and 10 under the additives section the term "bricresyl phosphate should 0 read --tricresyl phosphate At column ll, in Table 6, in the tabulation for Cu for Example the value O. 0" should read -O. 06-- gigned and salad this eleventh OF May 1976 [SEAL] Arrest.

RUTH C. MASON C. MARSHALL DANN 

1. A BASE STOCK SUITABLE FOR USE IN GAS TUBINE LUBRICANTS CONSISTING ESSENTIALLY OF: A. FROM ABOUT 20 TO ABOUT 80% BY WEIGHT OF THE BASE STOCK OF A COMBINATION OF (I) AN ISOPHTHALATE ESTER HAVING THE FORMULA:
 2. The base stock of claim 1 wherein said isophthalate ester is present in an amount from about 50 to about 80% and said oil is present in an amount from about 50 to about 20% by weight of the base stock.
 3. The base stock of claim 1 wherein R1 and R2 are each a C6-C12 alkyl group.
 4. The base stock of claim 3 wherein said adipate diester is derived from the esterification of adipic acid and an 80:20 molar mixture of isooctanol and isodecanol.
 5. The base stock of claim 1 wherein said adipate diester is di-2-ethylhexyl adipate.
 6. The base stock of claim 1 wherein said isophthalate ester is selected from the group consisting of di-2-ethylhexyl isophthalate, diisooctyl isophthalate, isooctyl isodecyl isophthalate, 2-ethylhexyl isodecyl isophthalate, diisodecyl isophthalate, and the ester of isophthalic and mixtures of C6-C12 straight chained alkanols.
 7. The base stock of claim 6 wherein the isophthalate ester is di-2-ethylhexyl iSophthalate.
 8. The base stock of claim 1 wherein said mineral oil has a viscosity in the range from about 5 to about 6.5 at 210* F.
 9. A gas turbine lubricant comprising the base stock of claim 1 and up to 5% by weight of the lubricant of a viscosity index improver.
 10. A gas turbine lubricant consisting essentially of the base stock of claim 1 and an oxidation inhibiting amount of a combination of (a) phenothiazine or derivative of phenothiazine and (b) a secondary diaryl amine.
 11. The gas turbine lubricant of claim 10 wherein said derivative of phenothiazine is N-ethyl dioctyl phenothiazine and said diaryl amine is p,p''-dioctyl diphenyl amine.
 12. The gas turbine lubricant of claim 10, which additionally contains an oxidation inhibiting amount of a methylene-linked hindered bisphenol.
 13. The gas turbine lubricant of claim 12 wherein said methylene-linked hindered bisphenol is 4,4''-methylene bis(2,6-di-t-butyl phenol).
 14. The base stock of claim 6 wherein said isophthalate ester is derived from isophthalic acid and a mixture of C6- C10 straight chained alkanols.
 15. The base stock of claim 6 wherein said isophthalate ester is derived from isophthalic acid and a mixture of C11- C12 straight chained alkanols. 